All internal combustion engines require a fresh charge of air and fuel. Gaseous air is mixed with fuel to form the charge. The fuel may be incorporated with the air prior to the being admitted into the combustion chamber by carburetion or fuel injection. Alternatively, the fuel may be injected into a charge of air in the combustion chamber at a point near the end of the compression stroke, as in a Diesel Cycle engine. There may be combinations of these two approaches as well.
Internal combustion engines may be generally classified as spark ignition or compression ignition engines. The well known Otto cycle is the basis for typical spark ignition engines and the Diesel cycle is the basis for compression ignition engines. internal combustion engines operate by admitting a charge of air or a fuel-air mixture during an intake phase or stroke of each cycle, compressing the charge during a compression phase or stroke, and causing the charge, with fuel added, to ignite to initiate a power phase or stroke. Products of combustion are ejected during an exhaust phase or stroke. Fuel may be added by inducing liquid fuel into air before the charge is admitted into the engine, as is the case, for example, with the well known methods of carburetion and fuel injection, as is the case with many Otto cycle engine applications. Gaseous fuels can also be injected into the incoming air stream as is the case with propane or Compressed Natural Gas (CNG). Alternatively, fuel may be injected into the combustion chamber at or near the end of the compression phase or stroke, as is the case with Diesel engines as well as many modern Otto cycle engines. Ignition occurs in response to an electrical spark timed to occur in the vicinity of the end of the compression stroke in Otto cycle engines. In Diesel cycle engines, ignition is initiated by the charge being superheated to the self-ignition temperature of the fuel at the point at which the fuel is injected.
Generally, internal combustion engines are benchmarked to function based on a stoichiometric ratio of fuel to air whereby there is only a slight excess of air needed for stoichiometric, or near complete, combustion to occur. Stoichiometric combustion disadvantages include a relatively high level of air pollution products of combustion, notably in the areas of oxides of nitrogen and unburned hydrocarbons. Aggravating the emissions, power, and efficiency parameters is that at the moment of ignition with the current art, the fuel-air charge is not prepared to the optimal temperature to maximize the benefits of the aforesaid parameters. “Lean burn” art has improved the emissions problem to a limited degree by providing an excess of air above stoichiometric requirements. However, the excess air typically also has a nominal temperature that is too low. As such, so much heat is absorbed by the cold air during combustion that there are problems with a slow flame front and incomplete combustion.
In Diesel cycle combustion, in particular, high charge pressures may contribute to heterogeneous mixing of air and fuel that may cause localized “hot pockets” of combustion. A result can be incomplete combustion with attendant unburned particulates and high levels of oxides of nitrogen. Additionally, very high compression ratios are required to superheat the air to temperatures required to evaporate and spontaneously combust injected fuel.
There remains a need for improvements in charge preparation for internal combustion engines that will mitigate the problems discussed above.